In a typical thermal printer, a thermal printing head is used to supply the heat to cause the transfer of dye from a dye bearing donor web to a dye receiver medium. The heating elements are controlled to transfer a variable amount of dye to the receiver. It is desirable to print at the highest speed possible while maintaining control over dye deposition. The typical time required to print a single line has decreased from over thirty milliseconds to about five milliseconds. As the speed has increased, the effective power delivered to the head has steadily increased. The higher amounts of power delivered to the head can affect the temperature of the head which will vary the amount of dye deposited. Accordingly, it will be appreciated that it would be highly desirable to maintain the print head at a constant temperature for consistent printing results.
Several methods have been used to control the print head temperature. U.S. Pat. No. 4,496,824, which issued Jan. 29, 1985 to Kawai et el., discloses a system that uses the head itself to raise the head temperature, and a fan to prevent overheating. U.S. Pat. No. 4,797,837 which issued Jan. 10, 1989 to R. M. Brooks, discloses a thermo-electric heater/cooler to control the temperature of the thermal head. U.S. Pat. No. 4,968,160, which issued Nov. 6, 1990 to Y. Ishizuka, discloses a heat pump to control the temperature of a thermal head. The temperature controlling fluid is contained in a closed loop with a layer of material between the head and the fluid. Accordingly, it will be appreciated that it would be highly desirable to have a simple apparatus to cool the print head wherein the cooling fluid directly contacts the heat producing portion of the print head.